This application is based on Application No. 2000-316514, filed in Japan on Oct. 17, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an automotive alternator, and in particular, relates to an outboard bearing construction for supporting a rotor.
2. Description of the Related Art
As the output of automotive alternators has increased, enlargement of rotors and increases in interior temperature have been promoted, requiring size reductions and high bearing reliability.
FIG. 13 is a longitudinal section of a conventional automotive alternator.
In FIG. 13, an inboard bracket 1 and an outboard bracket 2 are made of aluminum, formed into bowl shapes, and are fastened together by fastening bolts and nuts (not shown) with open portions of the bowl shapes facing each other. Cylindrical inboard and outboard bearing boxes 1a and 2a are formed integrally in central portions of end surfaces of the brackets 1 and 2. In addition, inboard and outboard ventilation apertures 1b and 2b are bored through the brackets 1 and 2 at outer circumferential portions of the bearing boxes 1a and 2a. 
A shaft 3 is rotatably supported in the brackets 1 and 2 by means of inboard and outboard bearings 4 and 5 disposed inside the bearing boxes 1a and 2a. A Lundell-type rotor 6 is fixed to the shaft 3 and disposed rotatably inside the brackets 1 and 2. In addition, a stator 7 is disposed with a first and second end thereof supported by the brackets 1 and 2 so as to surround the rotor 6.
Slip rings 8 for supplying field current to a field winding in the rotor 6 are fixed to an outboard end of the shaft 3, and a pair of brushes 9 are housed inside a brush holder 10 disposed inside the brackets 1 and 2 so as to slide in contact with the slip rings 8.
A pulley 11 and an external fan 12 are fixed to an inboard end portion of the shaft 3, and in addition, a rectifier 13 electrically connected to the stator 7 for converting alternating current generated in the stator 7 into direct current is mounted inside the outboard bracket 2.
In conventional automotive alternators constructed in this manner, an electric current is supplied from a battery (not shown) through the brushes 9 and the slip rings 8 to the field winding in the rotor 6, generating magnetic flux. Magnetic poles are generated by this magnetic flux in claw-shaped magnetic poles on the rotor 6. At the same time, rotational torque from an engine is transmitted through a belt (not shown) and the pulley 11 to the shaft 3, rotating the rotor 6. Thus, a rotating magnetic field is applied to a stator winding 7a, generating an electromotive force in the stator winding 7a. This alternating-current electromotive force passes through the rectifier 13 and is converted into direct current, charging the battery.
The external fan 2 is rotated and driven together with the rotation of the shaft 3, forming a cooling air flow in which external air flows in through the outboard ventilation apertures 2b, flows through the inside of the brackets 1 and 2, and is expelled through the inboard ventilation aperture 1b, cooling heat-generating parts such as the stator 7, the rotor 6, the rectifier 13, and a voltage regulator (not shown).
Now, as shown in FIG. 14, the outboard bearing 5 is constituted by a single-row bearing having a cylindrical inner ring 15 and a cylindrical outer ring 16, a ball track 17 disposed between the inner ring 15 and the outer ring 16, and a plurality of balls 18 disposed in the ball track 17. The inner ring 15 is fixed to the shaft 3, and the outer ring 16 is fixed to the outboard bearing box 2a. 
Thus, rotational torque from the engine is transmitted through the belt and the pulley 11 to the shaft 3, and the inner ring 15, which is fixed to the shaft 3, is rotated and driven with the shaft 3. A radial load due to tension applied to the belt is transmitted through the plurality of balls 18 to the outer ring 16. A load due to the weight of the rotor 6 is also transmitted through the plurality of balls 18 to the outer ring 16. By passing through the balls 18, these loads are applied to the outer ring 16 as vibrating loads, repeatedly giving rise to warping in the outer ring 16. Thus, one problem has been that fatigue failure occurs in the inner ring 15, the outer ring 16, and the balls 18, reducing the life of the outboard bearing 5.
In order to solve this problem, countermeasures have been taken to raise outer-ring rigidity by increasing the diameter of the bearing, substituting a bearing having a large load capacity, or thickening the wall of the outer ring. However, these countermeasures involve increasing the diameter of the outboard bearing 5, in other words, increasing the diameter of the outboard bearing box 2a, thereby reducing the size of the outboard ventilation apertures 2b. Similarly, the size of the rectifier 13 is also be reduced due to a necessity to ensure electrical insulation distance between the outboard bearing box 2a and the rectifier 13.
If the size of the outboard ventilation apertures 2b is reduced, the cooling air flow rate cannot be ensured, making the cooling of heat-generating parts such as the rotor 6, the stator 7, and the rectifier 13 insufficient, and if the size of the rectifier 13 is reduced, the area of a heat sink on the rectifier is reduced, making the cooling of the rectifier 13 insufficient, and as a result, the temperature of the automotive alternator rises, giving rise to reduced output and a deterioration in the life of component parts due to heat degradation.
Another countermeasure has been proposed in which the outboard bearing is constructed by lining up two single-row bearings, preventing fatigue failure by dividing the load in two. However, in that case, radial clearance in the two single-row bearings may differ, making the shared load in the two single-row bearings unbalanced, and a problem has been that bearing life is reduced.
Moreover, the inboard bearing 4 is constituted by a single-row bearing in a similar manner to the outboard bearing 5, but because the heat-generating parts such as the rectifier 13 and the voltage regulator are disposed at the outboard bracket 2 end, there is ample clear space on the outer circumferential side of the inboard bearing 4, and it is not necessary to ensure electrical insulation distance between a bearing box and a rectifier. Thus, it is possible to adopt a bearing having enlarged outside diameter, load capacity, or outer-ring wall thickness for the inboard bearing 4. Consequently, in an automotive alternator, countermeasures against fatigue failure are more important in the outboard bearing 5, which is where the heat-generating parts such as the rectifier 13 and the voltage regulator are disposed.
In conventional automotive alternators, because the outboard bearing 5 is constituted by a single-row bearing, one problem has been that warping is applied repeatedly, giving rise to fatigue failure in the outboard bearing 5, thereby reducing bearing life.
Fatigue failure in the outboard bearing 5 can be suppressed by adopting countermeasures in which rigidity is raised by increasing the diameter or the load capacity of the outboard bearing 5, or by thickening the wall of the outer ring. However, such countermeasures lead to reductions in the size of the outboard ventilation apertures 2b and the rectifier 13, increasing the temperature of the automotive alternator, and another problem has been that these countermeasures give rise to reduced output and a deterioration in the life of component parts due to heat degradation.
The present invention aims to solve the above problems and an object of the present invention is to provide an automotive alternator enabling the suppression of reductions in output and deterioration in working life as a result of temperature increases in the alternator by constituting an outboard bearing by a multi-row bearing having one inner ring and one outer ring, a plurality of ball tracks disposed axially between the inner ring and the outer ring, and a plurality of balls disposed in each of the ball tracks, thereby distributing the load bearing on the outer ring plurally in an axial direction, improving load-bearing properties without increasing the size of the outboard bearing, and enabling the size of the outboard bearing to be reduced while ensuring the durability thereof.
In order to achieve the above object, according to one aspect of the present invention, there is provided an automotive alternator including:
an inboard bracket formed in a bowl shape having a cylindrical inboard bearing box in a central portion of an end surface, and an outboard bracket formed in a bowl shape having a cylindrical outboard bearing box in a central portion of an end surface, the brackets being joined with open portions of the bowl shapes facing each other;
a shaft rotatably supported in the inboard and outboard brackets by means of inboard and outboard bearings disposed inside the inboard and outboard bearing boxes;
a pulley fixed to an inboard end portion of the shaft;
a stator disposed such that first and second ends thereof are supported in the inboard and outboard brackets;
a rotor fixed to the shaft, the rotor being disposed radially inside the stator;
a rectifier disposed in the outboard bracket on an outer circumferential side of the outboard bearing box; and
a heat exchange portion for dissipating heat generated in the rectifier,
wherein the outboard bearing is constituted by a multi-row bearing having one inner ring and one outer ring, a plurality of ball tracks disposed axially between the inner ring and the outer ring, and a plurality of balls disposed in each of the ball tracks.
According to another aspect of the present invention, there is provided an automotive alternator including:
an inboard bracket formed in a bowl shape having a cylindrical inboard bearing box in a central portion of an end surface, and an outboard bracket formed in a bowl shape having a cylindrical outboard bearing box in a central portion of an end surface, the brackets being joined with open portions of the bowl shapes facing each other;
a shaft rotatably supported in the inboard and outboard brackets by means of inboard and outboard bearings disposed inside the inboard and outboard bearing boxes;
a pulley fixed to an inboard end portion of the shaft;
a stator disposed such that first and second ends thereof are supported in the inboard and outboard brackets;
a rotor fixed to the shaft, the rotor being disposed radially inside the stator;
a rectifier disposed in the outboard bracket on an outer circumferential side of the outboard bearing box; and
a ventilation aperture bored through the outboard bracket on an outer circumferential side of the outboard bearing box,
the automotive alternator being constructed such that the rectifier is cooled by allowing air to flow through the ventilation aperture,
wherein the outboard bearing is constituted by a multi-row bearing having one inner ring and one outer ring, a plurality of ball tracks disposed axially between the inner ring and the outer ring, and a plurality of balls disposed in each of the ball tracks.
The rectifier may be constructed in an arc shape having a central angle of 180 degrees or more and may be disposed on a common axis with the outboard bearing so as to overlap the outboard bearing in a radial direction, and the ventilation aperture may be bored through the outboard bracket so as to open in an arc shape for half a circumference or more in a circumferential direction facing the rectifier.
Slip rings for supplying a field current to a field winding in the rotor may be disposed at an outboard end of the shaft, a diameter of the multi-row bearing and a diameter of the slip rings being constructed so as to be substantially equal.
The shaft may be supported in the multi-row bearing such that an outboard end surface of the shaft is positioned between an outboard end surface of the multi-row bearing and a center line of an outermost ball track at the outboard end.
A creep-preventing member may be disposed on an outer circumferential surface of the outer ring of the multi-row bearing facing the ball tracks.
The multi-row bearing may have two ball tracks, and the creep-preventing member may be formed into ring-shaped bodies having a width which is less than or equal to a diameter of the balls disposed in the ball tracks, the ring-shaped bodies being disposed on an outer circumferential surface of the outer ring facing each of the ball tracks such that width-direction center lines of the ring-shaped bodies are offset towards end surfaces of the multi-row bearing relative to center lines of the ball tracks.
The outboard bracket may be made of a metal, and the creep-preventing member may be made of a resin.
A heat dissipation means may be disposed in the outboard bracket.